skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Constraints for the aperiodic O-mode streaming instability

Abstract

In plasmas, where the thermal energy density exceeds the magnetic energy density (β{sub ∥} > 1), the aperiodic ordinary mode (O-mode) instability is driven by an excess of parallel temperature A = T{sub ⊥}/T{sub ∥} < 1 (where ∥ and ⊥ denote directions relative to the uniform magnetic field). When stimulated by parallel plasma streams, the instability conditions extend to low beta states, i.e., β{sub ∥} < 1, and recent studies have proven the existence of a new regime, where the anisotropy threshold decreases steeply with lowering β{sub ∥} → 0 if the streaming velocity is sufficiently high. However, the occurrence of this instability is questionable especially in the low-beta plasmas, where the electrostatic two-stream instabilities are expected to develop much faster in the process of relaxation of the counterstreams. It is therefore proposed here to identify the instability conditions for the O-mode below those required for the onset of the electrostatic instability. A hierarchy of these two instabilities is established for both the low β{sub ∥} < 1 and large β{sub ∥} > 1 plasmas. The conditions where the O-mode instability can operate efficiently are markedly constrained by the electrostatic instabilities especially in the low-beta plasmas.

Authors:
 [1];  [2];  [3];  [2];  [1]; ;  [3]
  1. Centre for Mathematical Plasma Astrophysics (CmPA), Celestijnenlaan 200B, 3001 Leuven (Belgium)
  2. (Germany)
  3. Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum (Germany)
Publication Date:
OSTI Identifier:
22407980
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 1; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANISOTROPY; ENERGY DENSITY; LIMITING VALUES; LOW-BETA PLASMA; MAGNETIC FIELDS; RELAXATION; TWO-STREAM INSTABILITY; VELOCITY

Citation Formats

Lazar, M., Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Schlickeiser, R., Research Department Plasmas with Complex Interactions, Ruhr-Universität Bochum, D-44780 Bochum, Poedts, S., Stockem, A., and Vafin, S., E-mail: mlazar@tp4.rub.de. Constraints for the aperiodic O-mode streaming instability. United States: N. p., 2015. Web. doi:10.1063/1.4905707.
Lazar, M., Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Schlickeiser, R., Research Department Plasmas with Complex Interactions, Ruhr-Universität Bochum, D-44780 Bochum, Poedts, S., Stockem, A., & Vafin, S., E-mail: mlazar@tp4.rub.de. Constraints for the aperiodic O-mode streaming instability. United States. doi:10.1063/1.4905707.
Lazar, M., Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Schlickeiser, R., Research Department Plasmas with Complex Interactions, Ruhr-Universität Bochum, D-44780 Bochum, Poedts, S., Stockem, A., and Vafin, S., E-mail: mlazar@tp4.rub.de. Thu . "Constraints for the aperiodic O-mode streaming instability". United States. doi:10.1063/1.4905707.
@article{osti_22407980,
title = {Constraints for the aperiodic O-mode streaming instability},
author = {Lazar, M. and Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum and Schlickeiser, R. and Research Department Plasmas with Complex Interactions, Ruhr-Universität Bochum, D-44780 Bochum and Poedts, S. and Stockem, A. and Vafin, S., E-mail: mlazar@tp4.rub.de},
abstractNote = {In plasmas, where the thermal energy density exceeds the magnetic energy density (β{sub ∥} > 1), the aperiodic ordinary mode (O-mode) instability is driven by an excess of parallel temperature A = T{sub ⊥}/T{sub ∥} < 1 (where ∥ and ⊥ denote directions relative to the uniform magnetic field). When stimulated by parallel plasma streams, the instability conditions extend to low beta states, i.e., β{sub ∥} < 1, and recent studies have proven the existence of a new regime, where the anisotropy threshold decreases steeply with lowering β{sub ∥} → 0 if the streaming velocity is sufficiently high. However, the occurrence of this instability is questionable especially in the low-beta plasmas, where the electrostatic two-stream instabilities are expected to develop much faster in the process of relaxation of the counterstreams. It is therefore proposed here to identify the instability conditions for the O-mode below those required for the onset of the electrostatic instability. A hierarchy of these two instabilities is established for both the low β{sub ∥} < 1 and large β{sub ∥} > 1 plasmas. The conditions where the O-mode instability can operate efficiently are markedly constrained by the electrostatic instabilities especially in the low-beta plasmas.},
doi = {10.1063/1.4905707},
journal = {Physics of Plasmas},
number = 1,
volume = 22,
place = {United States},
year = {Thu Jan 15 00:00:00 EST 2015},
month = {Thu Jan 15 00:00:00 EST 2015}
}
  • In collisionless plasmas, only kinetic instabilities and fluctuations are effective in reducing the free energy and scatter plasma particles, preventing an increase of their anisotropy. Solar energetic outflows into the interplanetary plasma give rise to important thermal anisotropies and counterstreaming motions of plasma shells, and the resulting instabilities are expected to regulate the expansion of the solar wind. The present paper combines quasilinear theory and kinetic particle-in-cell simulations in order to study the weakly nonlinear saturation of the ordinary mode in hot counter-streaming plasmas with a temperature anisotropy as a follow-up of the paper by Seough et al. [Phys. Plasmasmore » 22, 082122 (2015)]. This instability provides a plausible mechanism for the origin of dominating, two-dimensional spectrum of transverse magnetic fluctuations observed in the solar wind. Stimulated by the differential motion of electron counterstreams the O mode instability may convert their free large-scale energy by nonlinear collisionless dissipation on plasma particles.« less
  • The purely growing ordinary (O) mode instability for counter-streaming bi-Maxwellian plasma particle distribution functions has recently received renewed attention due to its importance for the solar wind plasma. Here, the analytical marginal instability condition is derived for magnetized plasmas consisting of equal-mass charged particles, distributed in counter-streams with equal temperatures. The equal-mass composition assumption enormously facilitates the theoretical analysis due to the equality of the values of the electron and positron (positive and negative ion) plasma and gyrofrequencies. The existence of a new instability domain of the O-mode at small plasma beta values is confirmed, when the parallel counter-stream freemore » energy exceeds the perpendicular bi-Maxwellian free energy.« less
  • The purely growing ordinary (O) mode instability has recently received renewed attention owing to its potential applicability to the solar wind plasma. Here, an analytical marginal instability condition is derived for counter-streaming bi-Maxwellian plasma particle distribution functions. The derived marginal instability condition as a function of the temperature anisotropy and plasma beta agrees remarkably well with the numerically determined instability condition. The existence of a new instability domain of the O-mode at small plasma beta values is confirmed with the leading A∝β{sub ∥}{sup −1}-dependence, if the counter-stream parameter P{sub e} exceeds a critical value. At small plasma beta values atmore » large enough counter-stream parameter, the O-mode also operates for temperature anisotropies A = T{sub ⊥}/T{sub ∥} > 1 even larger than unity, as the parallel counter-stream free energy exceeds the perpendicular bi-Maxwellian free energy.« less
  • The aperiodic ordinary (O-) mode instability in homogeneous and collisionless plasmas with kinetic anisotropies has recently received renewed attention due to its potential application in the solar wind, as well as for equal-mass plasmas. The present paper revisits the marginal instability condition of the O-mode derived from the electromagnetic linear dispersion equation for waves propagating perpendicular to the background magnetic field. For a counterstreaming bi-Maxwellian plasma system, this condition is found to be significantly affected by the streaming parameters. New functional dependencies (not studied before) of the counterstreaming parameters on the magnetic field and the other plasma parameters lead tomore » new conditions of this instability for the both equal mass and electron-proton plasmas.« less
  • The purely growing ordinary (O) mode instability driven by excessive parallel temperature anisotropy for high-beta plasmas was first discovered in the 1970s. This instability receives renewed attention because it may be applicable to the solar wind plasma. The electrons in the solar wind feature temperature anisotropies whose upper values are apparently limited by plasma instabilities. The O-mode instability may be important in this regard. Previous studies of O mode instability have been based on linear theory, but the actual solar wind electrons may be in saturated state. The present paper investigates the nonlinear saturation behavior of the O mode instabilitymore » by means of one-dimensional particle-in-cell simulation and quasilinear theory. It is shown that the quasilinear method accurately reproduces the simulation results.« less